<script>
  Person.prototype.say = function () {
    console.log('hello');
  };

  Person.prototype.age = 18;

  function Person() {
    this.name = '田总';
  }

  let p = new Person(); // 实例对象
  p.say();

  let p2 = new Person();
  console.log(p.age, p2.age);
</script>
